Resin/copper/metal laminate and method of producing same

ABSTRACT

A laminate for use in production of printed circuit boards comprising a metal layer having a first side and a second side; a metallic substrate, one side of the metallic substrate being attached to the first side of the metal foil; an adhesive substrate formed of a polymeric material having a first surface and a second surface, the first surface being attached to the second side of the copper foil, the adhesive substrate being at least partially uncured; and a releasable protective film along the second surface of the adhesive substrate.

FIELD OF THE INVENTION

The present invention relates generally to printed circuits, and moreparticularly, to components used in the manufacturing of printedcircuits and other articles.

BACKGROUND OF THE INVENTION

In the manufacture of printed circuits, namely printed circuit boards orcopper clad laminates, sheets of copper foil are typically bonded with adielectric layer of a partially cured epoxy resin impregnated with wovenglass fiber (conventionally referred to as a “pre-preg”) as in the caseof a circuit board, or onto another layer of foil as in the case ofcopper clad laminates. In both processes, the copper is etched toproduce conductive paths. It is extremely important to avoidcontamination of the copper foil sheets as any foreign matter, such asresin dust, fiberglass fibers, hair, grease, oil or the like, may resultin dots, dents, deposits or pits on the copper foil that can adverselyaffect the formation of the conductive paths forming the printedcircuits.

Contamination of a copper foil will typically occur at the differentprocessing steps the foil undergoes from its initial formation to itsuse in forming printed circuits. The initial forming of the copper foilwill of course affect the quality of the copper sheet. Thereafter, it isthe processing steps, particularly the manufacturing steps in preparingand bonding the copper foil sheet to a substrate or to another foilsheet, that generate substantial contamination that may affect the foil.For example, after the copper foil is produced, at some point it isusually cut into sheets. Cutting elements may create small metal sliversor shavings, or other machinery and materials used in the manufacturingprocess may be a source of other types of contamination, such as dust,grease or oil droplets, that may fall onto the surface of the foil andmay become imbedded therein as the foil passes over rollers and othersurfaces.

To protect the copper foil during subsequent handling and shipping, itis known to secure a metallic substrate to one side of the copper foilto protect same. For example, U.S. Pat. No. 5,153,050 to Johnstondiscloses a copper/aluminum/copper laminate wherein the shiny side of acopper foil is bonded along its peripheral edges to a clean sheet ofaluminum. U.S. Pat. No. 5,674,596 to Johnston further discloses securingcopper to a metallic substrate, such as a steel or stainless steelsubstrate.

By sealing the edges of copper and the metallic substrate with aflexible adhesive, the interior surface of the copper sheet is notexposed to airborne contaminants of the type previously described. Themetallic substrate basically functions as a protector, a carrier and aseparator for adjacent sheets of copper foil. Similarly, it has beenknown to adhere to the shiny side of the copper foil a protectivepolymeric film that may be removed during the assembly of the coppersheet onto a circuit board or onto another copper sheet.

The purpose of the foregoing laminate is to provide protection to theshiny side of the foil during subsequent operations. It is during theapplication of a bonding resin onto the matte side of the copper foil,and the subsequent application of the foil and resin onto a circuitboard or another sheet of foil, where contamination of the foil mayoccur. In this respect, basically, every processing step in formingprinted circuits or copper clad laminates has a potential for producingairborne contaminants or surface contaminants that may adhere to thesurface of the copper foil and that may interfere with the conductivelines to be etched therein. Thus, the elimination of any step betweenthe production of the copper foil and the ultimate bonding of thematerial to a circuit board or another copper foil would substantiallyreduce the likelihood of the foil being contaminated.

The present invention overcomes limitations in the prior art andprovides a copper foil having a metallic substrate adhered to one sideof a copper foil and a dimensionally stable, partially cured adhesivelayer secured to the other side of the copper foil, which adhesive layermay be later cured when the copper foil laminate is applied to a circuitboard or to another layer of copper foil as part of a copper cladlaminate.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a laminatefor use in the production of printed circuits boards and copper cladlaminates. The laminate is comprised of a copper foil layer having afirst side and a second side. A metallic substrate is attached to thefirst side of the copper foil layer by a band of adhesive extendingalong the periphery of the copper foil layer. An adhesive film formed ofa resinous material having a first surface and a second surface isapplied to the copper foil, with the first surface of the adhesive filmattached to the second side of the copper foil, wherein the secondsurface of the adhesive film faces away from the copper foil. The firstsurface of the adhesive film is substantially cured, and the secondsurface of the adhesive film is at least partially uncured. A releasableprotective layer extends along the second surface of the adhesive filmto protect same.

In accordance with another aspect of the present invention, there isprovided a method of forming a laminate for use in the production ofprinted circuit boards and copper clad laminates, the method comprisingthe steps of:

forming a metallic laminate by joining a surface of a copper foil to asurface of a metallic substrate by applying a band of flexible adhesivealong the periphery thereof;

applying a preformed, adhesive film onto the exposed surface of thecopper foil, the adhesive being formed of a substantially uncured,polymeric material having a releasable protective strip; and

curing the adhesive layer, wherein the outermost layer of the adhesiveadjacent the releasable protective layer is only partially cured.

In accordance with another aspect of the present invention, there isprovided a laminate for use in the production of printed circuit boardsor copper clad laminates. The laminate is comprised of a metal foillayer having a first side and a second side and a metallic substrate.One side of the metallic substrate is attached to the first side of themetal foil by a band of a flexible adhesive extending along theperiphery of the metal foil layer. An adhesive film formed of apolymeric material having a first surface and a second surface isprovided on the metal foil with the first surface being attached to thesecond side of the metal foil. The first surface of the adhesive film issubstantially cured, and the second surface is at least partiallyuncured. A releasable protective film is provided along the secondsurface of the adhesive substrate.

In accordance with another aspect of the present invention, there isprovided a method of forming a laminate for use in the production ofprinted circuit boards or copper clad laminates. The method comprisesthe steps of forming a metallic laminate by joining a surface of a metalfoil to a surface of a metallic sheet by applying a band of flexibleadhesive along the periphery thereof; applying a preformed adhesive ontoan exposed surface of the metal foil, the adhesive being formed of anuncured, dimensionally stable polymeric material having a releasableprotective layer, the adhesive being applied to the metal foil with thepolymeric material in contact with the foil; and curing the adhesive,wherein at least an outermost layer of the adhesive adjacent to thereleasable protective layer is only partially cured.

In accordance with another aspect of the present invention, there isprovided a laminate for use in production of printed circuit boards orcopper clad laminates. The laminate is comprised of a metal foil havinga first side and a second side. One side of the metallic substrate isattached to the first side of the metal foil by a material extendingalong the periphery of the metal foil layer. The material has adhesiveproperties to seal the facing interior surfaces of the metal foil andthe substrate. A film formed of a resinous material is attached to thesecond side of the metal foil, the film having a B-stage cure and havinga minimum dimensional thickness. A releasable protective film isprovided along the second surface of the adhesive substrate.

In accordance with another aspect of the present invention, there isprovided a method of forming a laminate for use in the production ofprinted circuit boards or copper clad laminates, comprising the stepsof: forming a metallic laminate by joining a surface of a metal foil toa surface of a metallic sheet by applying a material having adhesiveproperties along the periphery thereof, applying a preformed, adhesivefilm onto an exposed surface of the metal foil, the adhesive film beingformed of a substantially uncured, polymeric material on a releasableprotective film, the adhesive film being applied to the metal foil withthe polymeric material in contact with the foil; cutting the laminateinto sheets; and heating the laminate in a furnace at a predeterminedtemperature for a predetermined period of time to cure the adhesive filmto a B-stage cure.

In accordance with another aspect of the present invention, there isprovided a laminate for use in production of printed circuit boards orcopper clad laminates. The laminate is comprised of a metal foil layerhaving a first side and a second side. One side of the metallicsubstrate is attached to the first side of the metal foil by a band of aflexible, adhesive-like material extending along the periphery of themetal foil layer. A first resin layer of uniform thickness is providedon the metal foil, the first resin layer cured to a C-stage. A secondresin layer of uniform thickness is provided on the first resin layer,the second layer cured to a B-stage.

In accordance with another aspect of the present invention, there isprovided a method of forming a laminate for use in the production ofprinted circuit boards or copper clad laminates, comprising the steps offorming a metallic laminate by joining a surface of a metal foil to asurface of a metallic sheet by applying a band of flexible,adhesive-like material along the periphery thereof to join the metalfoil to the metallic sheet; applying a preformed, dimensionally stablefirst resin film onto an exposed surface of the metal foil, the firstresin film being formed of an uncured, first resin material; applying apreformed second resin film onto the first resin film; and heating themetallic laminate and the first and second resin layers to cause thefirst level to be cured to a C-stage and the second layer to be cured toa B-stage.

In accordance with another aspect of the present invention, there isprovided a laminate for use in production of printed circuit boards orcopper clad laminates, comprising a metal foil layer having a first sideand a second side; a metallic substrate, one side of the metallicsubstrate being attached to the first side of the metal foil along theperiphery of the metal foil layer; and an adhesive film formed of asubstantially uncured, polymeric material having a first surface and asecond surface, the first surface being attached to the second side ofthe metal foil.

In accordance with another aspect of the present invention, there isprovided a method of forming a laminate for use in the production ofprinted circuit boards or copper clad laminates, comprising the steps offorming a metallic laminate by joining a surface of a metal foil to asurface of a metallic sheet along the periphery thereof; applying apreformed, adhesive film onto an exposed surface of the metal foil, theadhesive strip being formed of a substantially uncured, polymericmaterial on a releasable protective strip, the adhesive film beingapplied to the metal foil with the polymeric material in contact withthe foil; and curing the adhesive film wherein at least an outermostlayer of the adhesive strip adjacent to the releasable protective layeris only partially cured.

In accordance with another aspect of the present invention, there isprovided a laminate for use in production of printed circuit boards orcopper clad laminates, comprising a metal foil having a first side and asecond side; a metallic substrate, one side of the metallic substratebeing attached to the first side of the metal foil along the peripheryof the metal foil layer to seal the facing interior surfaces of themetal foil and the substrate; a film formed of a resinous materialattached to the second side of the metal foil, the film having a B-stagecure and having a minimum dimensional thickness; and a releasableprotective film along the second surface of the adhesive substrate.

In accordance with a further aspect of the present invention, there isprovided a method of forming a laminate for use in the production ofprinted circuit boards or copper clad laminates, comprising the steps offorming a metallic laminate by joining a surface of a metal foil to asurface of a metallic sheet along the edges thereof; applying apreformed, dimensionally stable adhesive film onto an exposed surface ofthe metal foil, the adhesive film being formed of a substantiallyuncured, polymeric material, the adhesive film being applied to themetal foil with the polymeric material in contact with the foil; cuttingthe laminate into sheets; and heating the laminate in a furnace at apredetermined temperature for a predetermined period of time to cure theadhesive film to a B-stage cure.

In accordance with another aspect of the present invention, there isprovided a laminate for use in production of printed circuit boards orcopper clad laminates. The laminate is comprised of a metal foil havinga first side and a second side. One side of a metallic substrate isattached to the first side of the metal foil to seal the facing interiorsurfaces of the metal foil and the substrate. A layer formed of aresinous material is attached to the second side of the metal foil. Thelayer has a first surface and a second surface, the first surface of thelayer being attached to the second side of the metal foil and beingsubstantially cured, and the second surface of the layer being at leastpartially uncured.

It is an object of the present invention to provide a metal foillaminate for use in the manufacturing of printed circuit boards andcopper clad laminates.

Another object of the present invention is to provide a metal foillaminate as described above that has a metallic protective layer toprotect one side of the metal foil from contamination.

Another object of the present invention is to provide a metal foillaminate as described above that has a dimensionally stable, partiallyuncured resin layer on one side of the metal foil.

A still further object of the present invention is to provide a metalfoil laminate as described above, wherein a portion of the resin layerin contact with the metal foil is fully cured, and a portion of theresin layer facing away from the metal foil is only partially cured.

A still further object of the present invention is to provide a metalfoil laminate as described above having a removable protective layer onthe partially cured portion of the resin layer.

A still further object of the present invention is to provide a metalfoil laminate as described above, wherein the resin layer in contactwith the metal foil is fully cured.

A still further object of the present invention is to provide a metalfoil laminate as described above, wherein the metal foil is copper andthe metallic protective layer is aluminum.

A still further object of the present invention is to provide a processfor curing a resin layer on a metal foil, wherein the innermost portionof the resin layer in contact with the metal foil is fully cured, andthe outermost portion of the resin layer facing away from the metal foilis only partially cured.

These and other objects and advantages will become apparent from thefollowing description of preferred embodiments of the invention takentogether with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangement ofparts, embodiments of which are described in detail in the specificationand illustrated in the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a resin-coated copper laminateillustrating a preferred embodiment of the present invention;

FIG. 2 is an elevational, schematic view of a process line for forming aresin-coated copper laminate, as illustrated in FIG. 1;

FIG. 3 is a cross-sectional view of a resin-coated copper laminateillustrating an alternate embodiment of the present invention;

FIG. 4 is an elevational, schematic view of a process line for forming aresin-coated copper laminate, as illustrated in FIG. 3;

FIG. 5 is a cross-sectional view of a resin-coated copper laminateillustrating a still further embodiment of the present invention; and

FIG. 6 is an elevational, schematic view of a process line for forming aresin-coated copper laminate, as illustrated in FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings wherein the showings are for the purposeof illustrating preferred embodiments of the invention, and not for thepurpose of limiting same, FIG. 1 shows a metal/metal/resin laminate 20in accordance with one aspect of the present invention. Laminate 20 isfor use in the manufacturing of printed circuit boards and copper cladlaminates. Laminate 20 includes at least one metal foil sheet 22 mountedonto a metallic substrate 24, and a layer of a partially uncured resin26 that is provided on the outer surface of metal foil sheet 22. Whenultimately fabricated into a printed circuit or a copper clad laminate,metal foil sheet 22 is the material that forms the conductive paths, andresin layer 26 is the material used to secure metal foil sheet 22 onto adielectric layer (as in the case of a printed circuit board) or ontoanother layer of metal foil (as in the case of a copper clad laminate).Metallic substrate 24 is provided as a support element and as aprotective layer to protect metal foil sheet 22 from contamination, andis ultimately discarded during the manufacturing of a printed circuitboard or a copper clad laminate.

The use of a metallic substrate to protect a surface of a metal foilfrom contamination is disclosed in U.S. Pat. No. 5,153,050 to Johnstonand U.S. Pat. No. 5,674,596 to Johnston, the disclosures of which areexpressly incorporated herein by reference. As indicated in thosepatents, a laminate comprised of a metal sheet on a metallic substratemay be formed by applying a bead of a flexible adhesive 28 around theperipheral edge, i.e., the borders of the metallic substrate. Thepresent invention utilizes a laminate formed of a metal foil on ametallic substrate as generally disclosed in U.S. Pat. Nos. 5,153,050and 5,674,596, and adds a layer of an uncured, dimensionally stableresin 26 onto the exposed surface of the metal foil sheet.

In the embodiment to be hereinafter described, metal foil sheet 22 isformed of copper and metallic substrate 24 is formed of aluminum, andcopper foil sheets 22 are provided on each side of aluminum substrate 24to form a copper/aluminum/copper laminated component 40. It will beappreciated by those skilled in the art that metal foil sheet 22 may beformed of metal materials other than copper, such as, by way of exampleand not limitation, gold, nickel, silver, indium coated copper foil,nickel coated copper foil or the like. Further, it will also beappreciated that metallic substrate 24 may be formed of metallicmaterials other than aluminum, such as, by way of example and notlimitation, steel, stainless steel, brass, nickel alloy or the like.

Copper/aluminum/copper laminated component 40 is comprised of an inneraluminum substrate 24 having copper sheets 22 applied on each of thesurfaces thereof. (It will further be appreciated that metal sheet 22may be applied to only one side of metallic substrate 24.) Each ofcopper foil sheets 22 has a first side 22 a facing substrate 24 and asecond side 22 b facing away from aluminum substrate 24. First side 22 aof copper sheet 22 may be what is typically referred to in the art asthe “shiny side” of copper foil sheet 22. This side being the shiny sideformed on a smooth, polished metal drum during an electrodepositionprocess. Second side 22 b may be what is conventionally referred to the“matte side” of the copper foil, the matte side being the side of thefoil away from the drum in an electrodeposition process. As used herein,terms such as “shiny side” and “matte side” are used for the purpose ofillustration, and not for the purpose of limiting the present invention.First side 22 a (typically the shiny side) of copper foil sheet 22 isdisposed to face an uncontaminated surface of the aluminum substrate 24.In a preferred embodiment, copper foil sheets 22 are secured to aluminumsubstrate 24 by a continuous bead of flexible, adhesive-like material 28that extends around the peripheral edges, i.e., the borders, of thealuminum substrate. Resin-like material 28 may be an actual adhesive, ormay be a plastic material having adhesive properties. It will also beappreciated that copper foil sheets 22 may be secured to substrate 24along its periphery by means other than by adhesive without deviatingfrom the present invention. Other means of securing the periphery offoil sheets 22 to substrate 24 may be used so long as the facing,interior surface of foil sheets 22 is protected from contamination. Itwill also be appreciated that certain other types of copper foils suchas reverse treated or double treated foils will have a “matte side” ofthe foil disposed to face the uncontaminated aluminum.

According to the present invention, a uniform layer 26 of a resinmaterial is applied to second surface 22 b of copper sheet 22. Resinlayer 26 is preferably at least partially uncured. More preferably, theuncured portion of resin layer 26 is located at the outermost portionthereof at surface 22 b, and the innermost portion of resin layer 26,i.e., the portion of resin layer 26 at surface 22 a in contact with thecopper layer, is partially cured. Even more preferably, the innermostsurface of resin layer 26 is completely cured to bond resin layer 26 tocopper sheet 22. A removable protective layer 32 formed of a polymerfilm is provided over resin layer 26. Resin layer 26 preferably has athickness of about 0.5 mils to about 10.0 mils, and more preferably,about 1.0 mils to about 3.0 mils.

Referring now to FIG. 2, a process for forming laminate 20 isschematically illustrated. In FIG. 2, a copper/aluminum/copper laminatedcomponent 40 is conveyed along a predetermined path.Copper/aluminum/copper laminated component 40 is preferably formed inaccordance with aforementioned U.S. Pat. No. 5,153,050. In theembodiment shown, copper/aluminum/copper laminated component 40 is fedbetween two like feed rollers 62 on which a generally continuous ribbon54 of a resin is wound. According to the present invention, ribbon 54 isan uncured or substantially uncured resin material that is generallydimensionally stable under the exertion of stacking forces along itssurface. As used herein, the term “dimensionally stable” as applied tothe uncured resin material, shall mean the resin has properties whereinit will not significantly alter its shape or flow under the pressureexerted along its planar surface as a result of stacking pressure.Basically, it is intended that the term “dimensionally stable” asapplied to the resin film shall distinguish such film from layers ofuncured resin that flow when under the exertion of planar pressure.

A product manufactured and sold by Minnesota Mining & Manufacturing (3M)under the name “High Performance Epoxy Adhesive Bonding Film” findsadvantageous use as resin layer 26 in the production of laminate 20.This product is comprised of an epoxy resin and is available inthicknesses of 1 or 2 mils under 3M designations “9901” and “9902”respectively. The material is provided by the manufacturer withremovable protective polymer films 32 on both surfaces thereof. Thematerial has the following physical properties as disclosed by themanufacturer:

Property Units IPC Test Glass Transition* ° C. 180 CTE ppm/° C. 20°-110° C. 60 110°-180° C. 87 180°-250° C. 213 Peel Strength Lbs./inch8 2.4.9 Volatile Content % 1 2.3.37 Moisture Absorption % 1.7 2.6.2BChemical Resistance % >90 2.3.2 Dielectric Constant* 3.4 2.5.5.3Dissipation Factor* .022 2.5.5.3 Dielectric Strength Volts/mil 2200D-149 Insulation Resistance Megohms 1.00E+06 2.6.3.2 Volume ResistivityMegohms-cm 5.00E+07 2.5.17 Surface Resistivity Megohms 7.00E+05 2.5.17Solder Float Pass 2.4.13 Low Temperature Flexibility Pass 2.6.18Flexural Endurance Cycles 1787 3.7.4 Fracture Toughness Mpa*m ½ 0.65Modulus GPa 3.5 *Tests performed on heat resin.

In the process shown, protective polymer films 32 on the surface ofresin ribbons 54 facing copper/aluminum/copper laminated component 40are removed by a film take-up rollers 56. The inner layer of eachpolymer film is directed over idler rollers 58 onto take-up rollers 56.The removal of the inner layer of protective polymer films 32 exposesthe resin materials to the surfaces of copper foil sheets 22. Heated niprollers 62 force resin layers 26 and polymer films 32 onto the exposedsurfaces of copper 22 of copper/aluminum/copper laminated component 40,wherein resin layers 26 engages the matte sides of copper 22.Preferably, nip rollers 62 are heated sufficiently to warm resin layers26 to ensure positive contact with the exposed surfaces of copper sheets22.

In accordance with one aspect of the present invention,copper/aluminum/copper laminated component 40 with resin layers 26 andpolymer films 32 thereof are preferably conveyed in a continuous fashionpast heating elements, designated 72 in the drawings. Heating elements72 are operable to heat uncured resin layers 26. The heating of resinlayers 26 may be undertaken by conventional gas-fired or electric-firedheating means, but is more preferably performed by an induction heater,wherein the induction heating of the metallic layers, i.e., aluminumsubstrate 24 and copper sheets 22, heat resin layers 26 throughradiation and conduction as the heat radiates and is conducted to resinlayers 26 from copper/aluminum/copper laminated component 40. Heatingelement 72 is controlled such that resin layers 26 oncopper/aluminum/copper laminated component 40 are not fully cured. Inthis respect, the heating of resin layers 26 is preferably controlledsuch that resin layers 26 are cured to what is conventionally referredto in the art as “B-staged.” In this respect, it is conventionallyunderstood that an “A-staged” resin refers to a resin that issubstantially uncured. A “B-staged” resin refers to a resin that ispartially cured, although not fully cured. A “C-staged” resin refers toa resin that is substantially fully cured. Thus, in accordance with thepresent invention, in the embodiment shown in FIG. 2, resin layers 26 oncopper/aluminum/copper laminated component 40 are only partially curedto a B-stage. Laminate 20 then preferably passes between two nip rollers82. Continuous laminate 20 formed in accordance with the aforementioneddescribed process may then be cut into sheets 92, as schematicallyillustrated in FIG. 2, by a shearing blade 84. Depending upon the resinmaterial forming resin layers 26, continuous curing of resin layers 26may not be feasible in a continuous process of the type heretoforedescribed. An alternate method of curing resin layers 26 would be to cutlaminate 20 into sheets following the application of resin layer 26 ontocopper foil sheet 22, and to cure stacks of such sheets in a furnace ata predetermined time and temperature to cured resin layers 26 to aB-staged resin.

The process shown in FIG. 2 thus provides a copper/aluminum/copperlaminated component 40 having B-staged resin layers 26 of uniformthickness thereon, each resin layer 26 having a removable protectivepolymer film 32 covering resin layer 26. The present invention thusprovides a laminate 20 suitable for manufacturing printed circuit boardsand/or copper clad laminates. Laminate 20 has been described with aremovable protective film 32. It will be appreciated to those skilled inthe art that while such film 32 is preferable, laminate 20 may be formedwithout protective film 32 on resin layer 26. Laminate 20 is used byremoving protective polymer films 32 and attaching B-staged resin layers26 directly to pre-preg dielectric boards, or onto the surfaces ofcopper sheets on copper clad laminates. By providing a circuitmanufacturer with a B-staged resin layer 26 on copper sheet 22 thepossibility of contamination of copper sheet 22 during the processingrequired for shipping is reduced. With laminate 20, a circuitmanufacturer need only remove protective polymeric films 32 on resinlayers 26 and attach laminate 20 onto pre-preg dielectric or onto thesurfaces of circuits on copper clad laminates, and then heat B-stagedresin layers 26 until they are fully cured and are attached to thecircuit boards or to the surfaces of circuits on copper clad laminates.Thereafter, protective aluminum substrate 24 may be removed to exposeshiny sides 22 a of copper sheets 22. Copper sheets 22 may then beetched to produce desired circuit patterns for a printed circuit board,or another laminate 20 may be applied thereto to produce multi-layersfor a copper clad laminate. Laminate 20 thus facilitates simpler stepsin the manufacturing of printed circuit boards and copper cladlaminates, and eliminates possible contamination of copper sheets 22during shipment and subsequent processing.

Referring now to FIG. 3, a laminate 120 illustrating an alternateembodiment of the present invention is shown. Laminate 120 includes thesame copper/aluminum/copper laminated component 40 as shown in FIG. 1,and laminated component 40 is formed in the same manner as heretoforedescribed. Accordingly, elements of laminated component 40 as shown inFIG. 3 have been assigned the same reference numbers as like elements inFIG. 1. In accordance with this alternate embodiment, a first resinlayer 122 comprised of a first resin material is provided on theunexposed matte side surfaces 22 b of copper sheets 22. A second resinlayer 124, comprised of a second resin material, is applied to the outersurface of the first resin layer 122. A removable polymer protectivefilm 126 is provided on the exposed outer surface of second resin layer124. In accordance with this aspect of the present invention, the firstresin material forming resin layer 122 preferably has a curing ratedifferent from that of the resin material forming second layer 124. Morepreferably, the first resin material has a quicker curing rate than theresin material forming second layer 124, wherein first resin layer 122could be heated and cured to a C-stage, while second resin layer 124,when exposed to the same heat, would cure to a B-stage. Stated anotherway, laminate 120 is comprised of a copper/aluminum/copper laminatedcomponent 40 having first resin layers 122 on matte sides 22 b of coppersheets 22 that are fully cured and second resin layers 124, on firstresin layer 122, wherein second resin layers 124 are at least partiallyuncured, i.e., A-staged, B-staged or some mixture thereof. Removablepolymer films 126 are provided as protective barriers for the surfacesof second resin layers 124.

Referring now to FIG. 4, a process line for forming laminate 120 isshown. As indicated above, the inner portion of laminate 120 iscomprised of a copper/aluminum/copper laminated component 40 asheretofore described. Copper/aluminum/copper 40 is conveyed along a pathpast a first group 130 of rollers, wherein a feed roller 132 provides aribbon 134 of a first resin material that forms resin layers 122. Resinlayers 122 are provided between two polymer films 126. A pair of take-uprollers 136, 138 is provided to remove protective polymer films 126 onresin ribbons 134. Specifically, polymer films 126 on both sides ofresin ribbons 134 are fed over idler rollers 142 onto take-up rollers136, 138. First resin layers 122 are applied to copper/aluminum/copperlaminated component 40, and heated nip rollers 144 force first resinlayers 122 into surface engagement with copper sheets 22 ofcopper/aluminum/copper laminated component 40. Copper/aluminum/copperlaminated component 40 with first resin layers 122 thereon passesbetween a second group of rollers 150 that include resin ribbon feedrollers 152 on which ribbons 154 of the second resin material areprovided. Ribbons 154 have protective polymer films 126 on both sidesthereof. Feed rollers 152 provide ribbons 154 of second resin materialto form second resin layers 124 on laminate 120. Take-up rollers 156 areprovided to peel away polymer films 126 along the surface of resinribbons 154 that are to be brought into contact with first resin layers122. Specifically, polymer films 126 on the inner surface of resinribbons 154 pass over idler rollers 158 and are wound onto take-uprollers 156. Heated nip rollers 162 bring ribbons 154 of second resinmaterial into surface contact with the exposed surface of first resinlayers 122. As indicated above, outer protective polymer films 126 ofsecond resin layers 124 preferably remain on the upper exposed surfaceof second resin layers 124.

Composite laminate 120 is then preferably conveyed between heatingelements 172 of the type heretofore described. Heating elements 172 arepreferably controlled such that sufficient heat is provided to laminate120 to fully cure first resin layers 122 to a C-stage, but not so highas to cause second resin layers 124 to be fully cured. In this respect,second resin layers 124 are preferably heated to a B-stage. Followingthe heating, the respective layers and sheets of material pass betweennip rollers 174. As above, the generally continuous strip of laminate120 may be sheared by a cutting element 182 into sheets 184, asschematically illustrated in FIG. 4. As noted above with respect to theprevious embodiment, the resin materials used in resin layers 122, 124may not be suitable for curing in a continuous process. If so, sheetsmay be cut from laminate 120 following the application of resin layers122, 124 to copper sheets 22, and such sheets may be stacked and curedin a conventional furnace at predetermined times and temperatures tofully cure first resin layers 122 to a C-stage, but cure second resinlayers 124 to only a B-stage.

FIGS. 3 and 4 thus illustrate a laminate 120 and a method of formingsame, wherein the combined resin layers 122, 124 on copper sheets 22have a first portion in contact with a copper sheets 22 that is fullycured, and an outer exposed portion that is at least partially uncured.The uncured outer portion of the resin combined layers have removablepolymer films 126 whereby, upon removal of the polyfilm, the partiallyuncured, exposed portion of laminate 120 may be applied to dielectricboards as part of a printed circuit board or onto an exposed coppersheet as part of a surface laminate circuit. The application ofadditional heat will fully cure the outer portion of the combined resinlayer, i.e., will fully cure second resin layer 124, thereby securingcopper sheet 22 and resin layers 122, 124 onto either dielectricsubstrates or a copper clad laminate assembly.

Referring now to FIG. 5, a laminate 220 illustrating yet anotherembodiment of the present invention is shown. As with the foregoingembodiments, laminate 220 is comprised partially ofcopper/aluminum/copper laminated component 40 formed as discussed above.On copper sheets 22 of copper/aluminum/copper laminated component 40,resin layers 226 are applied. In FIG. 5, resin layers 226 are shown tobe thicker than the resin layers in FIGS. 1 and 3, solely for thepurposes of illustration. The showing of layers 226 is not intended toindicate a relative thickness. Protective polymer films 228 are providedon the outermost surfaces of resin layers 226.

In accordance with this embodiment of the present invention, theinnermost surface, i.e., the surfaces of resin layers 226 in contactwith copper sheets 22, are fully cured to a C-stage. The outermostsurfaces of resin layers 226 are at least partially uncured. Statedanother way, the outermost surfaces of resin layers 226 are uncuredA-stage, or a partially cured B-stage pre-preg or a mixture of both.More specifically, in the embodiment shown, a curing gradient existsfrom the innermost surface of resin layers 226, where the resin is fullycured, to the outermost portion of resin layers 226, where the resin isat least partially uncured. In FIG. 5, the curing gradient isgraphically illustrated by the shading of resin layers 226 wherein thedarker shading is intended to illustrate a more cured region of resinlayers 226 and a lighter region is intended to illustrate a less curedor uncured region of resin layers 226. Laminate 220 thus provides astructure wherein copper sheets 22 are fully bonded to a cured portionof resin layers 226, whereas the outer portions of resin layers 226 areat least partially uncured, thereby facilitating subsequent attachmentof resin layers 226 to either dielectric substrates or onto a copperpattern of copper clad laminates.

Referring now to FIG. 6, a process for forming laminate 220 isillustrated. As in the preceding embodiments, a copper/aluminum/copperlaminated component 40 is conveyed along a predetermined path. Feedrollers 232 having ribbons 234 of resin thereon are disposed on oppositesides of laminated component 40. Ribbons 234 are comprised of adimensionally stable, substantially uncured resin that forms resinlayers 226. As also indicated above, the resin typically has protectivepolymer film layers 228 on the opposite surfaces thereof. In theembodiment shown, take-up rollers 236 remove protective polymer films228 from the innermost surface of resin ribbons 234 so as to expose thesurfaces of the resin material to the surfaces of copper sheets 22.Specifically, polymer films 228 are removed from resin ribbons 234 andpass over idler rollers 238 and are wound onto take-ups 236. Contactrollers 242 force the exposed surfaces of the resin ribbons 234 onto thesurfaces of copper sheets 22 to form resin layers 226. Protectivepolyfilms 228 on the upper surfaces of resin layers 226 remain in place.Copper/aluminum/copper laminated component 40 with the resin layers 226and polymer film layers 228 thereon passes by heating elements 252 thatare provided to heat resin layers 226. In accordance with thisembodiment, heating elements 252 are induction heating devices to heatresin layers 226 by induction heating. Importantly, because thealternating magnetic field will not affect the resin layer, the heatingof resin layers 226 will be the result of heat radiated and conductedinto resin layers 226 as the metallic layers of copper/aluminum/copperlaminated component 40 heat up. In other words, the heat from the innermetal layers, i.e., copper sheets 22 and aluminum substrate 24 migrateoutward into adhesive layers 226 to heat same. According to the presentinvention, the induction heating of copper/aluminum/copper laminatedcomponent 40 is preferably done such that the temperature of the regionof resin layers 226 in contact with copper sheets 22 reach a temperaturewhereby these regions of resin layers 226 are fully cured to a C-stage,but the outer regions of resin layers 226, and specifically, at outersurfaces of resin layers 226, do not attain a temperature for asufficient length of time to fully cure such region, and therefore, theouter surfaces of resin layers 226 remain at least partially uncured,i.e., at an A-stage, a B-stage or a mixture of both.

To ensure that the outer surface regions of resin layers 226 do notreach a temperature wherein they will fully cure, the outer surfaces oflaminate structure 220 are preferably cooled. In the embodiment shown,composite laminate structure 220 passes through a chamber 262 whereinthe outer surfaces of laminate 220, specifically polymer films 228 andthe outer regions of resin layers 226, are cooled by exposure to acooling gas, such as the vapor of liquid nitrogen, wherein the gasmaintains the outermost surface regions of adhesive layers 226 at atemperature below their full curing temperature. In the embodiment shownin FIG. 6, spray fixtures 264 are schematically illustrated for sprayingliquid nitrogen into chamber 262 to cool the surfaces of laminate 220.As will be appreciated, other methods of chilling the outer surface ofresin layers 226 may be employed. For example, chilling rollers (i.e.,rollers having cold water flowing therethrough; not shown) may be usedand contact the outer surface of layers 226 to keep the same cool. Inthis respect, the method of cooling, in and of itself, is not criticalto the present invention. It is only important that the outer surfaceregion of resin layers 226 remain cool and does not reach a temperaturewherein the resin will fully cure.

As will be appreciated by those skilled in the art, the heating of theinner core of laminated component 40 of laminate 220 through inductionheating may be controlled in conjunction with the cooling of the outerregion of resin layers 226 to ensure that the innermost portion of resinlayers 226 in contact with copper sheets 22 of copper/aluminum/copperlaminated component 40 are substantially cured, thereby bonding resinlayers 226 to copper sheets 22, while the outermost regions of adhesivelayers 226 are at least partially uncured. In this respect, theoutermost regions of adhesive layers 226 may be completely uncured,i.e., an A-staged resin, or may be semi-cured, i.e., a B-staged resin ormay be a mixture of both. Following the cooling of the compositelaminate, the strip of laminate 220 may be cut or sheared into sheets asschematically illustrated in FIG. 6.

FIGS. 5 and 6 thus illustrate a laminate 220, and a method of formingsame, wherein laminate 220 has resin layers 226 bonded to copper sheets22 by fully cured resin regions, and outermost regions that are at leastpartially uncured, thereby enabling their attachment to dielectricsubstrates or onto other layers of copper clad laminates in a subsequentmanufacturing process. As indicated above, additional heating of resinlayers 226 will fully cure the resin, thereby securing resin layers 226(and ultimately copper sheets 22) onto the substrates or onto copperclad laminates.

The present invention thus provides a laminate structure for use inmanufacturing printed circuit boards and copper clad laminates, whereinthe assembly step of making the circuit board or the copper cladlaminate can be undertaken with a clean, uncontaminated copper foilsheet protected by the aluminum substrate. The copper foil sheet alreadyhas an adhering resin thereon, thereby eliminating additional processingsteps and the possibility of contamination of the copper foil duringsuch resin coating steps or other coating steps.

In the embodiments shown, the thicknesses of the respective materialshave, in some instances, been exaggerated for the purposes ofillustration. It should be noted that in keeping with the trend inelectronic circuitry, thinner and thinner materials are and will bepreferably used. By way of example and not limitation, as disclosed inthe foregoing embodiments, aluminum substrate 24 may have a thicknessranging from about 0.006 inches (6 mils) to 0.015 inches (15 mils) andcopper sheets 22 may have a thickness ranging from about ¼ ounce (about9 microns) to 2 ounces (about 70 microns). With respect to resin layers26, 122, 124 and 226 disclosed in the foregoing embodiments, such layersmay vary in thickness depending upon particular applications. Moreover,it should also be appreciated that although FIGS. 1 and 5 show laminateshaving a single resin layer, multiple layers of multiple types of resinmaterial may find advantageous application in formingresin/copper/aluminum laminates for use in the electronic industry.

As indicated above, a material available under the name “HighPerformance Epoxy Adhesive Bonding Film 9901/9902” manufactured byMinnesota Mining Manufacturing (3M) finds advantageous application tothe present invention, and provides a dimensionally stable, uncuredresin suitable for application in forming the laminate structuresdisclosed heretofore. Although the material heretofore described iscomprised of an epoxy, it will of course be appreciated that thecomposition of the resin material forming the resin layer may vary, andthat numerous materials may find advantageous application in laminatestructures used in the electronic industry.

Further, techniques for heating the resin layers to effect curingthereof may include electric resistance heating, gas or electricconvection heating, radiant heating, such as infrared or ultravioletheating, or the like. With respect to the process disclosed in FIG. 6,methods of heating wherein copper/aluminum/copper laminated component 40is first heated, and then through radiation and conduction, heat isradiated and conducted into resin layers 226 are preferred. As indicatedin the aforementioned description, induction heating would produce adesired heating of the metal core laminate, as would electricalresistance heating.

The foregoing description is a specific embodiment of the presentinvention. It should be appreciated that this embodiment is describedfor purposes of illustration only, and that numerous alterations andmodifications may be practiced by those skilled in the art withoutdeparting from the spirit and scope of the invention. It is intendedthat all such modifications and alterations be included insofar as theycome within the scope of the invention as claimed or the equivalentsthereof.

Having described the invention, the following is claimed:
 1. In a component for use in manufacturing printed circuit boards, the component comprised of a sheet of copper foil that is to be assembled onto a printed circuit board during manufacture of the printed circuit board and a sheet of metal to be discarded during the manufacture of the printed circuit board, said sheet of copper foil having an uncontaminated surface facing an uncontaminated surface of said sheet of metal, said surfaces of said sheets being in unattached contact with each other in an area that defines an uncontaminated central zone, the improvement comprising: a preformed adhesive epoxy resin film formed of a polymeric material having a first surface and a second surface, and having a volatile solvents content of about 1% in an uncured state, said film being attached to said component with said first surface in contact with a surface of said copper foil, wherein said resin film is cured while attached to said component such that at least said second surface of said resin film is only partially cured, said second surface being exposed.
 2. A component as defined in claim 1, further comprising a releasable protective film along said second surface of the adhesive epoxy resin film.
 3. A component as defined in claim 1, wherein copper foil sheets are provided on each side of a metallic substrate to form a copper-metal-copper laminated component.
 4. A component as defined in claim 3, wherein said metallic substrate is aluminum.
 5. A component as defined in claim 1, wherein a curing gradient exists from said first surface to said second surface of said adhesive epoxy resin film, said first surface being more cured than said second surface.
 6. In a component for use in manufacturing copper clad laminates, the component comprised of a sheet of copper foil that is to be assembled onto a copper clad laminate during manufacture of the copper clad laminate and a sheet of metal to be discarded during the manufacture of the copper clad laminate, said sheet of copper foil having an uncontaminated surface facing an uncontaminated surface of said sheet of metal, said surfaces of said sheets being in unattached contact with each other in an area that defines an uncontaminated central zone, the improvement comprising: a preformed adhesive film formed of a polymeric material having a first surface and a second surface, and having a volatile solvents content of about 1% in an uncured state, said film being attached to said component with said first surface in contact with a surface of said copper foil, wherein said resin film is cured while attached to said component such that at least said second surface of said resin film is only partially cured, said second surface being exposed.
 7. A component as defined in claim 6, wherein a curing gradient exists from said first surface to said second surface of said adhesive epoxy resin film, said first surface being more cured than said second surface.
 8. A component as defined in claim 6, further comprising a releasable protective film along said second surface of said adhesive epoxy resin film. 